a) Field of the Invention
This invention relates to a production process of an ABS resin and also to an ABS-polycarbonate resin composition making use of the ABS resin. In more detail, the present invention is concerned with a production process of an ABS resin having excellent impact resistance and capable of providing a molding good in weld strength and substantially improved in location-dependent gloss differences, with the ABS resin obtained by the production process, and also with an ABS-polycarbonate resin composition making use of the ABS resin and having good moldability, high resistance to thermal deteriorations, and improved in heat resistance and impact strength, especially impact resistance at low temperatures and the strength of ribbed portions.
b) Description of the Related Art
ABS resins have heretofore been produced by emulsion polymerization or continuous bulk or solution polymerization in general. Emulsion polymerization may not be preferred depending on the application, because the resultant ABS resin contains an impurity such as an emulsifier. In addition, a significant cost is needed to treat water, which is used in the polymerization, prior to its disposal. As a consequence, continuous bulk polymerization free of these problems has found increasing utility as a new production process. This invention is to significantly improve the quality by using such continuous bulk polymerization or continuous solution polymerization.
The present inventors have proceeded with an investigation to solve troublesome unevenness in the gloss of a molding, which is considered to be attributable to the development of a lower gloss at a location where no sufficient molding pressure is exerted during molding work (low-pressure portion). As a result, it has been surprisingly found that this problem can be completely solved by applying certain special conditions to continuous bulk polymerization and/or continuous solution polymerization.
The present inventors are not aware of any art which prior to the present invention, dealt with improvements of one or more steps in continuous bulk polymerization and/or continuous solution polymerization in an attempt to solve such a problem and is acknowledged to have brought about marked effects.
For example, Japanese Patent Publication No. SHO 49-7343/1974 discloses a process in which with a view to retaining impact resistance by an increased gel content upon reduction of the particle size of a rubbery polymer, provisional polymerization is conducted in a first polymerization reactor with the rubbery polymer being maintained in a state not converted into a dispersed phase and polymerization is then conducted in a second polymerization reactor to convert the rubbery polymer into a dispersed phase. This process however involves a problem in the theme of the invention of the present application that improvements be made in the uneven gloss of a molding of an ABS resin obtained by continuous bulk polymerization.
Japanese Patents Laid-Open Nos. SHO 63-118315/1988 and SHO 3-7708/1991, EP 477764(A), etc. also disclose processes improved over the so-called provisional polymerization process, in each of which in a multi-reactor polymerization process making use of two or more reactors, conversion of a rubbery polymer into a dispersed phase is conducted in the second reactor. These process are however still insufficient for improving the uneven gloss of a molding of an ABS resin obtained by continuous bulk polymerization.
Further, Japanese Patent Laid-Open No. HEI 7-233204/1995 discloses a process in which a plug flow reactor is used as a first polymerization reactor to conduct provisional polymerization with a rubbery polymer being maintained in a state not converted into a dispersed phase and polymerization is then conducted in a second polymerization reactor to convert the rubbery polymer into a dispersed phase. This process is however not intended to improve such uneven gloss of a molding of an ABS resin, which is obtained by continuous bulk polymerization and/or continuous solution polymerization, as dealt with in the invention of the present application, although it is superior in impact resistance and gloss to processes which primarily use a back-mixed stirred tank reactor and are often employed in continuous bulk polymerization and/or continuous solution polymerization.
Japanese Patent Laid-Open No. HEI 6-192346/1994 discloses a process, in which rubber particles are formed using a special rubber component of the branched form in a plug flow reactor as a first polymerization reactor and their particle sizes are then adjusted using a particular shear machine. This process is however not preferred, because it additionally requires the shear machine so that the process steps and facilities become more complex. In addition, this process cannot achieve improvements in such uneven gloss as dealt with in the invention of the present application, since it is an object of this art to make improvements in impact resistance and gloss and no sufficient homogeneity can be achieved in the particle size of a rubbery polymer by a mechanical particle size adjustment making use of such a shearing machine.
The invention of the present application is to provide a process which does not specifically require any particular shearing machine.
Incidentally, ABS-polycarbonate resin compositions are known as resin compositions having excellent heat resistance and impact resistance, and are used as molding, materials.
Keeping in step with the wide-spread use of these compositions as large and thin-wall molding materials and high-speed injection molding materials in recent years, these conventional compositions have developed increasing problems because they exhibit low fluidity during molding and hence have low moldability and require long time for molding. In addition, as the range of applications of moldings becomes greater owing to the move toward moldings with thinner walls, there is an increasing need for the impartation of impact resistance, especially low-temperature impact resistance.
Improvements have also been proposed with a view to achieving these themes.
For example, Japanese Patent Laid-Open No. SHO 62-240352/1987 discloses, at page 1, lower left column, line 12 to page 2, upper right column, line 20, a process in which with a view to reducing a deterioration in the impact strength of a cracked molded piece, a graft copolymer is blended with an aromatic polycarbonate. This graft copolymer is obtained by graft-copolymerizing a rubbery polymer with two or more monomers selected from aromatic vinyl monomers, cyanated vinyl monomers or alkyl methacrylates. The content of the rubbery polymer is 60 wt. % or higher, the grafting degree the rubbery polymer is 50% or lower, and the intrinsic viscosity of a non-grafted resin component is 0.6 dl/g or lower.
The above process however still requires an improvement in mechanical strength, especially rigidity or heat resistance because of a high content of a rubbery polymer in an ABS resin. For the adoption of emulsion polymerization, an additive such as an emulsifier is needed and in addition, treatment of waste water is also needed, resulting in complex steps. The process is therefore still accompanied by problems to be solved from the standpoint of economy. Further, the process failed to bring about any substantial improvement in low-temperature impact resistance.
Further, Japanese Patent Publication No. SHO 62-39176/1987 discloses, at page 2, left column, line 39 to right column, line 42, a process in which the low-temperature impact strength of a polycarbonate is improved by blending two types of ABS resins having different rubber particle sizes and grafting degrees which fall within specific ranges, respectively.
However, this process is also disadvantageous from the industrial standpoint because it becomes complex due to the need for the separate production of the two types of ABS resins of different compositions and their subsequent blending with the polycarbonate. In addition, the process is still not considered to be sufficient with respect to the improvement of low-temperature impact strength.
Japanese Patent Laid-Open No. SHO 61-148258/1966 discloses, at page 1, lower right column, line 10 to page 2, lower right column 15, a process in which two types of ABS resins different in rubber content, one having a high rubber content and the other a low rubber content, and, if necessary, an AS resin are blended to improve the balance among heat resistance, impact resistance and moldability.
However, to produce an ABS resin of a high rubber content and high grafting degree, limitations are unavoidably imposed on its production process. In particular, application of bulk polymerization is difficult. Moreover, like the above-mentioned processes, this process also become complex because of the need for the separate production of the two types of ABS resins and optionally, the one type of AS resin and their blending with a polycarbonate.
As has been described above, it is the object of the present invention to provide a production process of an ABS resin having novel functions so that a molding can be obtained with reduced unevenness in gloss and with well-balanced excellent properties. It is also the object of the present invention to provide an ABS-polycarbonate resin composition of superb physical properties by blending the ABS resin in a polycarbonate.
With a view to achieving the above-described objects, the present inventors have proceeded with an extensive investigation, leading to the present invention. Namely, the present invention provides a process for the continuous production of an ABS resin, including a step of polymerizing 100 parts by weight of a monomer component, which is composed of a styrene monomer and an acrylonitrile monomer or of a mixture thereof and a vinyl monomer copolymerizable with at least one of the monomers, in the presence of 4 to 50 parts by weight of a rubbery polymer by continuous bulk and/or continuous solution polymerization to form a polymer of the monomer component as a continuous phase and particles of the rubber polymer as a dispersed phase, wherein:
(1) the polymerization step comprises at least two substeps, one being a first-stage substep of forming particles of the rubbery polymer and the other being a second-stage substep of adjusting the particle sizes of the particles;
(2) the first-stage polymerization substep as the particle forming substep is conducted in a polymerization system making use of a plug flow reactor or a batch polymerization reactor, and conducts polymerization at least until the particles of the rubbery polymer are formed in the polymerization mixture; and
(3) the second-stage polymerization substep as the particle size adjusting substep increases a converted amount of the monomer component into the polymer compared with that in the particle forming substep and makes smaller the particles of the rubbery polymer formed in the particle forming substep.
This invention also provides an ABS-polycarbonate resin composition comprising:
(I) 100 parts by weight of a thermoplastic polycarbonate, and
(II) 10 to 500 parts by weight of an ABS resin; wherein
1) the ABS resin (II) is available by the above-described process,
2) the ABS resin (II) comprises 5 to 30 wt. % of the rubbery polymer,
3) a polymer component (A) in the ABS resin (II), said polymer component (A) being available by elimination of insoluble components from the ABS resin (II) through extraction of the ABS resin (II) at 25xc2x0 C. with a 7:3 (by weight) mixed solvent of methyl ethyl ketone and methanol, comprises 8 to 30 wt. % of an acrylonitrile component,
4) the polymer component (A) has a reduced viscosity (xcex7sp/c) of from 0.2 to 0.65 dl/g, and
5) the rubbery polymer comprises at least butadiene parts, and a grafting degree of a styrene/acrylonitrile copolymer on the butadiene parts of the rubbery polymer in the ABS resin (II) ranges from 55 to 200%.